Isolation of A. galli eggs from adult female worms A batch of A. galli eggs was obtained according to a method described by Permin et al. (1997 a ). In short, the hens were slaughtered and adult female A. galli collected from the small intestine. The worms were dissected and their uteri transferred to a Petri dish where the eggs were squeezed out using a wooden spatula. Tissue debris were removed and the eggs mixed with a small amount of tap water. The eggs were counted and the suspension diluted to contain 2500 eggs/ml and then divided into two portions. One portion was stored at 5°C to prevent embryonation of the eggs. Two days later, this portion was used to evaluate the effect of Stalosan F on nonembryonated A. galli eggs. The second portion was stored in 0.1 N sulphuric acid at 18°C for 5 weeks until the eggs were embryonated in order to study the effect of the disinfectant on the infective L 3 -stage of A. galli . Experiment 1: in vitro treatment and examination The effect of in vitro treatment with Stalosan F was examined and compared with commercial bird sand as control for all four batches of parasite eggs: 1) newly excreted non-embryonated mixed eggs; 2) embryonated mixed eggs; 3) freshly extracted nonembryonated A. galli eggs; and 4) embryonated A. galli eggs. A 300 l egg suspension (~750 eggs) was spread over a layer of neutral agar in labelled Petri dishes. Stalosan F or bird sand was then sprinkled evenly over the egg suspension in the Petri dishes at a concentration of 100 g/m 2 and incubated at 18°C for 1, 2, 3, 7 or 21 days (see Table 1). After the required exposure time the eggs were washed off the Petri dishes in tap water. The disinfectant or sand was subsequently removed by a light spin in the centrifuge leaving the eggs in the supernatant. The eggs were examined under microscope and judged either as “normal appearing” or “abnormal”. The experiment was done in triplicate. Experiment 2: Experimental infections A batch of parasite eggs was made to evaluate the effect of Stalosan F on the infectivity of newly excreted mixed parasite eggs. Half of the batch was, together with the disinfectant (100 g/m 2 ), applied over a layer of neutral agar in large Petri dishes and incubated at 18°C for one week, after which the parasite eggs were washed in tap water and then incubated in 0.1N sulphuric acid at 18°C. The other half of the batch was treated similarly, except that commercial bird sand was used instead of the disinfectant. After 4 weeks of further incubation (i.e. a total of 5 weeks), the eggs were counted and diluted to contain 1000 eggs/ml in both batches and two groups of 25 parasitenaive chickens, 4 weeks of age, were subsequently inoculated with 500 eggs. Group 1 received the Stalosan F -treated eggs and group 2 received the untreated eggs. All animals were slaughtered 8 weeks after inoculation, and their intestines examined for the presence of parasites (Permin and Hansen, 1998).
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